This invention concerns a useful fluoroelastomer composition and a process for curing a fluoroelastomer composition.
Fluoroelastomers are known to be useful in specialized areas, such as high temperature-resistant gaskets, seals, diaphragms, and tubing. Fabricated fluoroelastomer articles can withstand temperatures of about 250.degree.-350.degree.C while retaining their good elasticity.
It is necessary for many applications, for example gaskets for high-temperature reactors, that the fluoroelastomer article be resilient and have low compression set. This is accomplished by curing the article; that is, by vulcanizing or cross-linking the elastomer.
The industries which manufacture and use fluoroelastomer compositions for the production of cured fluoroelastomer articles are in need of a new fluoroelastomer vulcanization process (and a fluoroelastomer composition for use therein) which makes it possible to combine satisfactory cure rates with good processing safety, good storage stability and reasonable cost of the unvulcanized formulations; and which yields vulcanized articles of good stress/strain properties and low compression set. There is also a need in many applications for such a process which enables one to produce cured articles which are relatively soft and rubbery as well as low in compression set. Furthermore, there is a need in various applications for a process which permits the use of economical formulations having a relatively high filler content in the manufacture of cured articles having low compression set and good stress/strain properties.
It is known that fluoroelastomers can be cured by using an aromatic hydroxylic compound as a vulcanization agent. One such compound is 4,4'-sulfonyldiphenol. When using this compound, one can make cured fluoroelastomer articles having excellent physical properties (e.g. desirable stress/strain values and low compression set values). This compound is also relatively low in cost. However, the cure rates obtainable with 4,4'-sulfonyldiphenol have been considerably slower than one can obtain with such aromatic hydroxylic compounds as hexafluoroisopropylidene-bis (4-hydroxybenzene) which is relatively expensive. Therefore, in spite of its low cost, 4,4'-sulfonyldiphenol has had very little use by those who manufacture cured fluoroelastomer articles.